The proposed research is an investigation of information processing in nerve fibers innervating the guitarfish vestibular receptors. It has two main objectives: (1) the characterization of dynamic responses as obtained by applying engineering input-output analytical techniques, and (2) the determination of explicit receptor mechanisms as the bases for the dynamic response characteristics. Isolated labyrinth preparations have been used to obtain "open-loop" afferent response characteristics in the absence of a functioning efferent system. The proposed research extends this work to the intact in vivo guitarfish, equipped with a semi-chronic recording apparatus. The results of this research will be a test of hypotheses concerning the influence of an intact efferent system on afferent response dynamics. The role of electrical events occurring inside vestibular receptors is investigated by intra-receptor recording and stimulating micropipettes. These studies will correlate local electrical field potentials with both information-rich stimuli and afferent response recordings. The results from these studies will be used to test hypotheses concerning biophysical mechanisms of transduction in vestibular responses. Finally, the responses from vertical semicircular canals will be compared with those obtained previously from horizontal semicircular canals, in order to test an hypothesis concerning the dynamic matching of these responses with behavioral movements.